Zonked-out is a slang term that refers to a state of extreme tiredness or exhaustion. Antonyms for this word include alert, awake, energetic, refreshed, and invigorated. For instance, if you wake up from a good night's sleep, you feel refreshed and energized, which is the exact opposite of feeling zonked-out. Similarly, after drinking a strong cup of coffee or taking a power nap, you may feel alert and awake, which is a complete opposite of feeling tired or zonked-out. Therefore, the choice of antonym would depend on the specific situation or circumstances in which zonked-out is used.